riscv: Get rid of riscv_pfn_base variable

Use directly phys_ram_base instead, riscv_pfn_base is just the pfn of
the address contained in phys_ram_base.

Even if there is no functional change intended in this patch, actually
setting phys_ram_base that early changes the behaviour of
kernel_mapping_pa_to_va during the early boot: phys_ram_base used to be
zero before this patch and now it is set to the physical start address of
the kernel. But it does not break the conversion of a kernel physical
address into a virtual address since kernel_mapping_pa_to_va should only
be used on kernel physical addresses, i.e. addresses greater than the
physical start address of the kernel.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Tested-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20230324155421.271544-2-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: Alexandre Ghiti

arch/riscv/include/asm/page.h

@@ -91,8 +91,7 @@ typedef struct page *pgtable_t;
 #endif
 
 #ifdef CONFIG_MMU
-extern unsigned long riscv_pfn_base;
-#define ARCH_PFN_OFFSET		(riscv_pfn_base)
+#define ARCH_PFN_OFFSET		(PFN_DOWN((unsigned long)phys_ram_base))
 #else
 #define ARCH_PFN_OFFSET		(PAGE_OFFSET >> PAGE_SHIFT)
 #endif /* CONFIG_MMU */

arch/riscv/mm/init.c

@@ -271,9 +271,6 @@ static void __init setup_bootmem(void)
 #ifdef CONFIG_MMU
 struct pt_alloc_ops pt_ops __initdata;
 
-unsigned long riscv_pfn_base __ro_after_init;
-EXPORT_SYMBOL(riscv_pfn_base);
-
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
 pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
 static pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
@@ -285,7 +282,6 @@ static pmd_t __maybe_unused early_dtb_pmd[PTRS_PER_PMD] __initdata __aligned(PAG
 
 #ifdef CONFIG_XIP_KERNEL
 #define pt_ops			(*(struct pt_alloc_ops *)XIP_FIXUP(&pt_ops))
-#define riscv_pfn_base         (*(unsigned long  *)XIP_FIXUP(&riscv_pfn_base))
 #define trampoline_pg_dir      ((pgd_t *)XIP_FIXUP(trampoline_pg_dir))
 #define fixmap_pte             ((pte_t *)XIP_FIXUP(fixmap_pte))
 #define early_pg_dir           ((pgd_t *)XIP_FIXUP(early_pg_dir))
@@ -985,7 +981,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	kernel_map.va_pa_offset = PAGE_OFFSET - kernel_map.phys_addr;
 	kernel_map.va_kernel_pa_offset = kernel_map.virt_addr - kernel_map.phys_addr;
 
-	riscv_pfn_base = PFN_DOWN(kernel_map.phys_addr);
+	phys_ram_base = kernel_map.phys_addr;
 
 	/*
 	 * The default maximal physical memory size is KERN_VIRT_SIZE for 32-bit